In this study we study a wide variety of mesons in the context of a transition from a hadron resonance gas (HRG) to a quark gluon plasma (QGP).
Such a phase transition takes place through the overlap of hadrons and should accompany the chiral restoration and deconfinement.
The HRG in magnetic fields were studied in Refs.[1]}, [2]} using hadron spectra in the Particle Data Group (PDG) [3]}
with the hadronic Zeeman couplings to magnetic fields.
This approach should be valid for weak magnetic fields \(eB \ll \Lambda _{\rm QCD}^2\) , but at larger \(B\)  the structural changes in hadrons should be taken into account.
In this respect the structural changes make some mesons lighter but the others heavier than predicted by the HRG model based on the PDG,
and hence (except in the large \(B\)  limit) it is not readily apparent how magnetic fields affect bulk thermodynamic quantities such as pressure and entropy.
Global analyses of meson spectra are necessary and a simple quark model is suitable for this purpose.
Including all the above-mentioned effects we find that the entropy is indeed enhanced considerably by magnetic fields, provided that the dynamical quark masses remain \(\sim \Lambda _{\rm QCD}\)  for a wide range of \(B\) .
